The present invention relates to an optical waveguide used in optical communication or the like. Further, the present invention particularly relates to a method of fabricating a polymer optical waveguide substrate having a structure of a V-groove for fiber alignment used in mounting an optical fiber to an optical waveguide.
In recent years, with an object of high function formation and small-sized formation of an optical module for communication, there is investigated an optical module using a silica optical guide. Already, an optical splitter or an arrayed-waveguide-grating wavelength multiplexer and demultiplexer or the like using a silica optical waveguide has been reduced to practice. Further, there has been realized a small-sized optical transmitter and receiver module at a low cost by mounting in hybrid, a semiconductor element such as a laser diode or a photodiode on a substrate having a silica optical waveguide. In the meantime, as a material of constituting an optical waveguide, other than silica, polymer resin, that is, polymer has also been investigated. A polymer optical waveguide can be formed by spin coating and therefore, the polymer waveguide is provided with productivity higher than that of a silica optical waveguide and a waveguide substrate can be fabricated at a low cost. Therefore, by using a polymer waveguide in place of a quartz waveguide, drastic low cost formation of the module can be expected. According to the optical module, it is necessary to optically couple an optical waveguide and an optical fiber with low loss. Normally, when a single mode fiber used in optical communication is used, it is necessary to position and fix positions of an optical waveguide and an optical fiber with submicrometer accuracy in order to couple the optical waveguide and the optical fiber with low loss. In order to carry out the operation in a short period of time and at a low cost, there has been investigated to integrate a groove in a shape of V for aligning an optical fiber on a silicon substrate forming the optical waveguide. As examples of forming a V-groove for fiber alignment at a silicon substrate having a silica optical waveguide, there are, for example, Japanese Patent Laid-Open No. 197178/1997, Japanese Patent Laid-Open No. 29638/1996, Proceedings of the 1996 IEICE (The Institute of Electronics, Information and Communication Engineers) General Conference, vol. Electronics 1, SC-2-8, p. 444 and the like.
As an example of forming a polymer optical waveguide after a V-groove has already been fabricated on a substrate, there is pointed out Japanese Patent Laid-Open No. 288717/1998. Further, there is disclosed a method of separately fabricating, positioning and pasting together a polymer optical waveguide and a V-groove structure in Japanese Patent Laid-Open No. 202158/1999 or Japanese Patent Laid-Open No. 47055/2000.
It is a first object of the embodiment of the present invention to provide an optical waveguide member easy to fabricate at low cost.
It is a second object of the embodiment of the present invention to provide a method of fabricating an optical waveguide member easy to fabricate at low cost.
Particularly, it is an object of the embodiment of the present invention to provide a structure of an optical waveguide member having a polymer optical waveguide substrate having a V-groove and capable of achieving excellent optical coupling by minimizing an increase in loss between an optical fiber and an optical waveguide caused by a nonuniformity in a film thickness of resin.
According to a representative first mode of the embodiment of the present invention, there is provided an optical waveguide member characterized in comprising at least a groove portion in a shape of V, a silicon substrate having a flat region opposed to the groove portion in the shape of V by interposing a second groove portion in a direction of extending the groove portion in the shape of V, an optical waveguide provided along the groove portion in the shape of V, a first resin layer constituting a core layer of the optical waveguide and a second resin layer constituting a clad layer of the optical waveguide above the flat region, wherein thicknesses of the first and the second respective resin layers are reduced at a vicinity of an end face of the flat region opposed to the first groove portion and the shape of the groove in the shape of V is set such that when an optical fiber is mounted to the V-groove in the shape of V, a height of a center of a core of the optical fiber becomes a height lower than a height of a center of the core of the optical waveguide at a portion thereof at which the film thickness more remote from the boundary than the groove in the shape of V is substantially flat. Further, the flat region opposed to the groove portion in the shape of V by interposing the second groove portion, constitutes a portion raised in a projected shape in view from the groove portion having the shape of V. The same goes in the following.
According to a second representative mode of the embodiment of the present invention, there is provided an optical waveguide member characterized in comprising at least a groove portion in a shape of V, a silicon substrate having a flat region opposed to the groove portion in the shape of V by interposing a second groove portion in a direction of extending the groove portion in the shape of V, an optical waveguide provided along the groove portion in the shape of V and opposedly to a predetermined wall face of the second groove portion, a layer of an adhering material, a third resin layer constituting a first clad layer of the optical waveguide, a first resin layer constituting a core layer of the optical waveguide and a second resin layer constituting a second clad layer of the optical waveguide above the flat region, wherein thicknesses of the first, the second and the third respective resin layers are reduced at a vicinity of end faces thereof opposed to the first groove portion.
According to a representative third mode of the embodiment of the present invention, there is provided an optical waveguide member characterized in that an optical waveguide is formed at a portion above a silicon substrate, a core or a clad of the optical waveguide is constituted by a polymer resin, the silicon substrate includes a groove in a shape of V for positioning and fixing an optical fiber to the optical waveguide and a groove extended in a direction orthogonal to the groove in the shape of V at a boundary of the optical waveguide, a film thickness of the core or the clad constituting the optical waveguide becomes thinner at a vicinity of the boundary than other portion thereof and when the optical fiber is mounted to the V-groove in the shape of V, a height of a center of a core of the optical fiber becomes a height lower than a height of the core of the optical waveguide at a desired position from the boundary. In this case, the shape of the groove in the shape of V is designed to constitute a height achieving highly efficient optical coupling between the optical fiber and the optical waveguide.
Main modes of a method of fabricating an optical waveguide member according to the embodiment of the present invention are as follows.
According to a first mode of a method of fabricating thereof, there is provided a method of fabricating an optical waveguide member which is a method of fabricating an optical waveguide member having at least an optical waveguide a core or a clad of which is constituted by a polymer and a groove in a shape of V for positioning and fixing an optical fiber to the optical waveguide above a silicon substrate, the method is characterized in the steps of forming the groove in the desired shape of V directed in a longitudinal direction of the optical fiber at the silicon substrate, thereafter, forming the optical waveguide by coating polymer resins for the optical waveguide and removing the polymer resin films at a region of mounting the optical fiber.
According to a second mode of the method of fabricating thereof, there is provided the method of fabricating an optical waveguide member according to the above-described, characterized in that after forming the optical waveguide, there is formed a groove for dividing the region of optical waveguide and the region of mounting the optical fiber therebetween, successively, polymer resin films of the region of mounting the optical fiber is removed.
According to a third mode of the method of fabricating thereof, there is provided the method of fabricating an optical waveguide member according to the above-described, characterized in that after forming the groove in the desired shape of V directed in a longitudinal direction of the optical fiber at the silicon substrate, there is provided an adhering layer for promoting an adhering performance between the silicon substrate and the polymer at a region of the silicon substrate for leaving a polymer layer, successively, the optical waveguide is formed.
According to a fourth mode of the method of fabricating thereof, there is provided a method of fabricating an optical waveguide member characterized in comprising a step of forming a groove portion in a shape of V at a silicon substrate, a step of forming a layer of an adhering material at an upper face of a region which is a flat region constituting the groove portion in the shape of V and is present in a direction of progressing light of the optical waveguide, a step of forming a first resin layer constituting a core layer of the optical waveguide and a second resin layer constituting a clad layer of the optical waveguide by covering at least upper faces of the groove portion in the shape of V and a flat region constituting the groove portion in the shape of V of the silicon substrate prepared in this way, a step of forming a second groove portion having a wall face opposed to an end face of the optical waveguide and a step of removing a part of at least the first and the second respective resin layers above the groove region.